When designing an irrigation system, the objective is always the same: to use water and energy as efficiently as possible. For centre pivots specifically, a set of core considerations provides the framework for achieving an optimal design.
The first step in any irrigation system design is to determine how much water the customer has available. This will have an effect on what area can be irrigated, crop choice and system choice. When irrigating from a borehole, we need to ensure the hole is tested and can deliver the water continuously. Â
The system should be able to deliver enough water to sustain optimal crop growth at the peak requirement. Crop water requirements depend on the area, crop type, growth stage and time of year/season. Pivot sprinkler packages will typically range from 8 – 14 mm/24 hours, but systems running on solar power might have packages as high as 24 mm/24 hours. There are however limitations in this regard as higher delivery rates cause higher instantaneous application rates and may cause run-off.
It is important to keep the system efficiency in mind as not all the water we pump to the pivot will get to the plant’s root zone. The SABI published efficiency for a centre pivot is in the region of 85%. This means that in order to deliver 10 mm to the soil, we will need to irrigate roughly 11.8 mm.Â
We always try to optimise the area usage, but larger pivots are not always better. Pivots larger than about 50 ha have long circle times, limit the sprinkler package size and have high instantaneous application rates at their ends increasing the risk of run-off. These factors can make management and scheduling difficult. Larger pivots also have a higher inlet pressure which means that to irrigate 50 ha with one pivot will require more energy than two 25 ha pivots.Â
Span dimensions should also be considered: the optimal pipe diameter is the size where you strike the best balance between upfront cost (buying a larger pipe) and long-term running cost (energy lost due to friction).
The largest expense over the lifetime of an irrigation system is the energy cost to deliver the water to the pivots. When an irrigation system comprises many centre pivots, the water delivery system design can have many shapes and forms. The final design choice has to be practical, easy to manage and optimise energy requirements.Â
Here, the obvious choice is not always the best: one or several big pumps delivering water through a connected network of pipes often wastes a lot of energy. Any pressure delivered to a pivot that is more than its requirement at that moment wastes energy. Spending more time and money on an efficient system initially will definitely pay off in the long run.
Choosing the latest technology when it comes to sprinklers is one of the most important parts of irrigation design, as it directly affects both yield and water-usage. The ideal pivot system, has the correct sprinkler package, which means:
Irrigation design can be overwhelming and complex when it’s new. That is why it is always recommended to work with an experienced irrigation designer to survey, plan, and install your irrigation system. At Agrico, we focus on the technicalities so you can focus on farming. Â
Agrico has a strong team of engineers specialising in irrigation system design, pump set design, pipework and pump station layouts. Our designs aim to optimise efficiencies, realise energy savings, simplify installation and increase the return on investment of the project.
For more information about Agrico’s innovative irrigation solutions, call +27 21 950 4111, email info@agrico.co.za, or visit www.agrico.co.za.
Drawing on Agrico’s extensive experience in irrigation design, this article explores the key considerations behind creating efficient, reliable irrigation systems, from water availability and crop requirements to pivot sizing, energy consumption and sprinkler selection.
Absa AgriBusiness has partnered exclusively with Agrico to offer qualifying clients preferential finance on new pivot irrigation systems, with interest rates from as low as prime less 2%. The partnership provides farmers with flexible repayment structures, faster turnaround times and access to Agrico’s extensive irrigation service network across Southern Africa.
With 440 hectares of bananas under irrigation, Inyoni relies on a precisely engineered irrigation system to meet the high water demands of its crop. Working closely with Agrico, the farm has developed innovative solutions tailored to the unique conditions of Komatipoort.
Op die diep sandgronde van die Noord-Vrystaat bly die resep vir sukses eenvoudig: maak die grond oop, laat die wortels dieper groei en benut elke druppel water ten volle. Met die Agrico T-reeks skeurploeg word die grond se potensiaal volledig ontsluit, een hektaar op ’n slag.
In samewerking met Agrico-kundiges is dit nou vir Carl en Cawood Crous moontlik om water met sonkrag van rivier na dam te pomp, en met behulp van gravitasie na hul spilpunte te vervoer.
Elke druppel water wat op die plase Kromvlei en Vrede, in die distrik Piketberg gebruik word, tel. As deel van die Karsten-groep se boerdery, word watertoediening op beide plase wetenskaplik en met deeglike beplanning aangepak. Hul vennoot in dié proses, is Agrico.
